Many vehicles are built to include, or are retrofitted to include, telematics functionality. This functionality enables a module within the vehicle to communicate wirelessly with remote entities of interest such as call centers, vehicle service providers, emergency responders, friends, family, and so on. While this functionality provides high levels of convenience and peace of mind to vehicle users, it is also occasionally susceptible to the disconnections and disruptions that affect other network communications. Such disruptions, while usually correctable, may result in a diminished user experience and impaired user satisfaction due to delay, lost data, and so on. Therefore, it is generally desirable to eliminate such disruptions or to ensure that reconnection occurs as quickly as possible.
Typically, telematics units communicate wirelessly via packets, i.e., via a packet data connection. One such connection type sometimes used is CDMA 1xRTT, which is also at times referred to as CDMA2000 1x since the CDMA 1xRTT protocol is a phase of CDMA2000, a proposed 3G service that conforms to the ITU IMT-2000 standard for UMTS (Universal Mobile Telecommunications System) services for delivering near-broadband data over a mobile network. The CDMA 1 XRTT protocol can be implemented via minor hardware and software modifications relative to existing CDMA infrastructures.
As a packet-based extension to CDMA networks, CDMA 1xRTT can theoretically support data rates as high as 153 kbit/s. However, in practical implementations, the maximum data rate may vary, and may be as low as 9.6 kbit/s. Thus, the need for minimizing interruptions and delay due to disconnection is still present.
A substantial portion of the delay inherent in the use of CDMA 1xRTT and other technologies such as CDMA 1xEVDO can be traced to the retry mechanism used therein. In particular, upon detection of disconnection, current retry schemes within this protocol are designed to retry the packet connection in the following failure modes: Traffic channel assignment failure, PPP connection failure, and TCP/IP connection failure. This presents two limitations in the conventional tethered mode packet call between the DTE (TCU) and the ME (NAD) up to the DCE (Network). In particular, the DTE may not have knowledge of prior failure modes due to either lack of failure signals from the ME or simple implementation of the application timer. Moreover, the failure modes may be from any layer while establishing the packet session. The tethered mode architecture cannot support retries selectively for both failure modes on the protocol layers and failure modes on the application layer. This exacerbates the problems and user dissatisfaction caused by disconnection, in that reconnection may be delayed or even precluded.